Xenogeneic antibodies with reactivity for surface determinants of the guinea pig line-10 hepatocarcinoma were isolated using cellular-immunoadsorbents prepared by coupling formalin treated line-10 cells to diethylaminoethyl cellulose. Antibodies prepared in this manner exhibited a high degree of reactivity for line-10 surface determinants but also reacted with surface determinants of the syngeneic line-1 hepatocarcinoma. Further restriction of antibody reactivity was accomplished by passage of the antibodies through cellular-immunoadsorbents prepared with syngeneic line-1 hepatocarcinoma cells. These antibodies bound to line-10 cells but showed significantly reduced reactivity for line-1 cells and no reactivity for guinea pig spleen cells or for an unrelated murine EL-4 lymphoma. The sequential use of immunoadsorbents is an additional method to prepare "tumor-specific" antibodies. An attempt was made to isolate antigens shared by cells of the line-10 guinea pig hepatocarcinoma and BCG. Line-10 associated antigens in the ascites fluid of line-10 bearing animals were passed through immunoadsorbents to which "purified" xenogeneic anti-BCG (anti-BCG-P) had been coupled. Components in ascites fluid that bound to anti-BCG-P were eluted and were shown to bind to antibodies in rabbit antisera that were raised against BCG and line-10 cells. These antigenic components were designated Sh-ag and consisted primarily of proteins. Antibodies to Sh-ag produced in rabbits reacted with high specificity to line-10 and BCG surface antigens. Following a sequence of immunochemical procedures, components with common antigenic determinants were also isolated directly from line-10 cells and from BCG. These experiments confirmed that an antigenic relationship existed between line-10 cells and BCG and that shared antigenic components could be isolated by immunochemical procedures and partially characterized.